1. Field of the Invention
The present invention relates to an image process method for correcting an image signal, an image process apparatus adopting the above method, and a storage medium storing a program to execute the above method. More particularly, the present invention relates to an image process apparatus for decreasing a color noise, an image process apparatus adopting the above method, and a storage medium storing a program to execute the above method.
2. Related Background Art
In recent years, as hard-copy technology, especially a full-color hard-copy technology, develops, an excellent image reproduction can be achieved by using printing technology such as an inkjet recording system and the like and a high-pixel digital camera. By recording materials and image processes, color reproduction evolves up to extent by which digital photographing provides with an equal reproduction ability with silver bromide photographing.
However, there is a drawback that a color noise due to a characteristic of an image pickup element or the like in an input apparatus might be included in the image itself which should be printed. For example, there is a drawback that a noise due to a dark current in a CCD element, a fixed pattern noise, a noise on a signal line due to color signal transmission, and the like occasionally mix with the input image.
In order to eliminate the above drawback, Japanese Patent Application Laid-Open No. 5-153608 (simply called JPA '608: corresponding to U.S. Pat. No. 5,432,869) describes that, by obtaining an average of upper and lower dye data adjacent to a notable pixel along the vertical direction, the dye data is subjected to smoothing filtering in the vertical direction without deteriorating image brightness.
Further, JPA '608 describes that, by detecting the correlation of the brightness of continuous three pixels along the vertical direction, an edge part where a change in the brightness along the vertical direction is extreme according to the correlation of the brightness is considered to be the part where also a change in the dye data is large, and thus the smoothing filtering is decreased for such the part. Conversely, when the change in the brightness along the vertical direction is small, the smoothing filtering is increased. Further, JPA '608 describes a method for expanding, by repeating an operation to obtain the above average for the notable pixel several times, the smoothing for the dye data along the vertical direction with simple structure.
However, when such the conventional color noise elimination as above is applied to an image signal, apparent (or seeming) resolution of texture on the image not detected easily only by the edge from the brightness signal might be deteriorated. Further, when chromaticity of an attentional color noise is greatly different from surrounding chromaticity, there is a problem that it is necessary to repeat a color noise elimination process several times for the notable pixel.
In recent years, from the viewpoint of desirable color reproduction, an input image is first analyzed by a printer driver or the like, and processes such as brightness correction, saturation (or chroma) emphasis and the like are performed to the input image itself in accordance with the analysis result. For example, Japanese Patent Application Laid-Open No. 10-200777 describes that an image is first analyzed, and then a process for appropriate saturation correction is performed.
Further, when an image taken by a low-pixel digital camera is printed, such the printed image might be overshadowed by the printed image taken by the above high-pixel digital camera, whereupon a method of enlarging or expanding the input image to a suitable size by using anti-aliasing technique such as a bicubic manner, a nearest neighbor manner or the like is known.
Further, the noise such as the color noise or the like due to the dark current in the CCD element is included in the digital camera image. In color reproduction based on a subtractive color mixture system used in a hard copying machine, a gray line is very unstable frequently, and gradation is occasionally reversed around the gray line. Thus, since the color which should be originally the gray replaces the color around the gray line because of a color noise, there is a problem that it becomes easy for such the reversal part as above to appear on the printed image.
As a process to reduce the color noise, a color noise reduction process to divide a video signal into a brightness signal and a color difference signal in a TV set and clip the amplitude in the frequency band corresponding to the color noise part of the color difference signal is known.
However, if the image correction processes such as the brightness correction, the saturation emphasis and the like according to the analysis result, the enlargement process and the noise reduction process are combined, following problems are caused.
Namely, since the saturation of the entire image is emphasized according to the image correction processes such as the saturation emphasis and the like, the effect of the color noise reduction process might not be able to be demonstrated about the emphasized color noise part.
Further, since the input image is subjected to the enlargement process, the effect of the color noise reduction process might not be able to be demonstrated about the enlarged color noise part.